Furnace for hot air heating systems



Dec. 10, .1963

Filed July 11, 1961 H. M. BLUMENSHINE El AL 3,113,565

FURNACE FOR HOT AIR HEATING SYSTEMS 3 Sheets-Sheet l I INVENTORS A06 4% izmj/m/f Dec. 10, 1963 H. M; BLUMENSHINE ETAL 3,113,565

v FURNACE FOR HOT AIR HEATING SYSTEMS Filed July 11, 1961 s Sheets-Sheet 2 ArmP/MK 1963 H. M. BLUMENSHINE EI'AL 6 FURNACE FOR HOT AIR HEATING SYSTEMS Filed July 11, 1961 s Sheets-Sheet 3 i J J 5% 5i T K a Q m. Q

INVENTORS. bww M @Z/MfA/jM/VE BY 400150 EZUZK United States Patent Office 3,il3,5fi Patented Dec. lb, 1%63 3,113,565 FURNAE FGR HGT AER HEATENG SYSTEMS Hugh M. iBiurnenshiue, Whi tier, and Leo Bloch, Monterrey frarlr, (Salli, assignors to The Siegler Qorporation, Pasadena, (Satin, a corporation of Delaware Filed .luly 11, 1961, Ser. No. 123,144 5 Claims. (Cl. 12691) The invention relates to a furnace for hot air heating systems.

Conventional furnaces for hot air heating systems are designed to accept flow of heating air past the heat exchanger portion in a vertical direction of flow for some applications and in a horizontal direction of flow for other applications. This presents the disadvantage of the necessity for different furnaces for air flow in a vertical direction and for air flow in a horizontal direction with consequent increased manufacturing expense and inventory investment. Conventional furnaces may also be expensive to manufacture because they require a large number of different parts and because such parts are shaped so that fabrication thereof into the complete furnace is time consuming and expensive. Moreover, conventional furnaces frequently have a venturi and mixing chamber extending rom the throat of the vent-uiri which are located exteriorly of the furnace proper and therefore present un- Wieldiness of the furnace and undesirable installation problems. The above problems presented by conventional furnaces and the solution thereof by the inventive apparatus will be apparent from the following description of the inventive apparatus.

The inventive apparatus consists, broadly, of a furnace com rising a firebox tunnel defining an interior burner chamber, a flue tunnel defining an interior chamber for flow of gases, and a plurality of plate-like heat exchanger elements extending between the firebox tunnel and the flue tunnel and extending laterally on each side of the firebox tunnel and the flue tunnel. The firebox tunnel and time tunnel lie in a common plane and are spaced from each other and parallel to each othe Each heat ex changer element is symmetrically disposed on each side of the firebox and flue tunnels, and the several heat exchanger elements are spaced from each other along such tunnels. Each heat exchanger element is comprised of a pair of identical plate-like members having a central body portion and an edge portion circumscribing the central body portion and dished laterally from the central body portion. The edge portion includes a flange lying in a single plane which extends transversely to the firebox tunnel and flue tunnel. The flanges on each pair of plate-like members in each heat exchanger element are connected together to define an interior chamber within the heat exchanger elenient for flow of gases. A burner is disposed in the burner chamber of the firebox tunnel and extends approximately the length of the firebox tunnel. The burner defines an intrior chamber extending its length and closed at on end of the burner and open at the other end of the burner and also pairs of laterally aligned burner head openings in opposite sides of the burner with a pair of such burner head openings aligned with the interior chamber of each heat exchanger element. A constricted flow passage defining a venturi threat is disposed in the interior chamber of the burner adjacent to its open end and between such open end and the first pair of burner head openin s with a venturi throat extension extending from the throat of the venturi inwardly in the interior chamber of the burner in spaced relation from the walls of such chamber. The venturi throat extension defines a flow passage for gases approximately equal to the constricted flow passage through the venturi throat at the junction of the extension and the VCHtUlI'i throat and gradually increases in flow passage area to discharge into the chamber within the burner. The discharge end of the extension is spaced from the closed end of the chamber of the burner and from the walls of such chamber to define a plenum chamber in the burner chamber for equalization of gas pressure. A burner head is disposed in each burner head opening and communicates from the chamber within the burner to the exterior of the burner head with the discharge end of the burner head having a burner grid which defines a plurality of elongated apertures extending in the same direction as the extent of the heat exchanger elements between the firebox tunnel and the flue tunnel so that a fan-like flame emanates from the burner heads. The firebox tunnel defines openings communicatingeuveen the interior chamber in each heat exchanger element to each burner head with each such opening permitting the fan-shaped flame from each burner head to flare into the chamber within each heat exchanger element. The line tunnel defines a plurality of openings communicating between its interior chamber and the interior chamber of each heat exchanger element for flow of gases from within each heat exchanger element to the chamber in the flue tunnel.

With the above apparatus, heating air may be directed through the heat exchanger elements either in a direction transverse to the common plane of the taxes of the firebox and line tunnels or in a direction parallel to such plane, this being permit ed by the unique shape of the firebox tunnel, flue tunnel, and heat exchanger elements, so that the furnace is adapted for four-way air flow, that is, air flow either transverse to the common plane of the axes of the firebox and flue tunnels or parallel thereto and in either direction of flow. hioreover, since the plate-like members defining each heat exchanger element are identical and symmetrical there is no right and left hand platelikc member for each heat exchanger element, but rather one die is used to make both halves of each heat exchanger element with consequent large savings in manufacturing costs. The flanges extending about each heat exchanger element ermit the two halves thereof to be seam welded by machine processes rather than b hand with further substantial savings in manufacturing costs. Also, the unique arrangement of the venturi extension disposed Within the burner tube [results in a more compact furnace and one which lends itself more readily to various installations without the above described disadvantages of conventional furnaces which have the venturi and venturi extension disposed exteriorly of the furnace proper.

The invention will be fully understood from a reading of the following description in conjunction with the accompanying drawings, in which:

FIG. 1 is a elevational view of the inventive apparatus;

PEG. 2 is a sectional View along the line 2-2 in FIG. 1;

FIG. 3 is an elevational View of a portion of the inventive apparatus;

FIG. 4 is a plan View of the portion of the apparatus shown in FIG. 3; and

FIG. 5 is a sectional view along the line 55 in FIG. 3.

Referring to FIG. 1, M denotes an elongated firebox tunnel, and 11 denotes an elongated flue tunnel spaced from the firebox tunnel and parallel thereto. Firebox tunnel 10 is made of sheet metal or the like and comprises a generally semi-cylindrical housing 12 having outwardly extending flanges 13 and 14 (FIG. 2) extending along its length. A cover plate 15 overlies flanges 13, 14 on housing 10 and is connected to such flanges in conventional manner, as by spot welding or sheet metal screws, to define an interior burner chamber extending the length of firebox tunnel it One end of the firebox tunnel is closed with cap 16 secured to housing 12 in partially broken away conventional manner, as by means of sheet metal screws 17 and 18. The other end 1) of firebox tunnel is open. Flue tunnel 11 is constructed in generally the same manner as firebox tunnel it) and is a sheet metal structure comprised of a generally semi-cylindrical housing 19 having outwardly extending flanges 20, 21 extending its length. A cover plate 22 extends between and engages flanges 26 21 and is connected to such flanges in conventional manner, as by spot welding or sheet metal screws, to define an interior chamber in flue tunnel 11 for flow of gases. A cap 23 is secured to one end of flue tunnel 11 by means of sheet metal screws 24, 25 to close such end of the flue tunnel. The other end 26 of the flue tunnel is open for connection to a vent duct in conventional manner for conveyance of combustion gases to the exterior of the structure in which the furnace is utilized. The longitudinal center lines of firebox tunnel 10 and flue tunnel 11 lie in a common center line plane, denoted at 27 in FIG. 2, and are disposed symmetrically on each side of such plane 27, this orientation and symmetry of the firebox and flue tunnels being an important aspect of the invention as will be apparent below. Firebox tunnel 1i? and flue tunnel 11 extend through suitable receiving apertures in plate 28 adjacent one end of the firebox and flue tunnels and in plate 29 adjacent the other end of the firebox and flue tunnels and are held rigidly in the above described orientation relative to each other by means of such apertures in plates 28,. 29. Plate 29 is shown generally in plan in FIG. 2, and plate 28 is generally similar thereto.

A plurality of heat exchanger elements 40, 41, and 42 extend between firebox tunnel ill and flue tunnel 11 and are spaced from each other along such tunnels. Heat exchanger elements 4fi, 41, and 42 are identical, and it is to be understood that whatever is described with respect to one applies equally with respect to the others. Heat exchanger element 42 is a hollow sheet metal platelike member having a generally rectangular shape in plan view as shown in FIG. 2 and extends symmetrically on each side of firebox tunnel 1t and flue tunnel 11 so that it is symmetrical in all respects on each side of com mon center line plane 27 of the firebox and flue tunnels. Each heat exchanger element is comprised of a pair of identical plate-like members, indicated at 43 and 44 for heat exchanger element 42, which have a central body portion dished inwardly at 45, 46, 47, and 48 for members 44, 43, respectively, to define a relatively shallow flow passage 49 for flow of gases through the heat exchanger element. Shallow flow passage 49 extends the full width of the heat exchanger element transverse to the common plane of the firebox and fine tunnels as indicated with the bend lines 59, 51 in FIG. 2. The purpose of shallow flow passage 49 is to produce etficient heat transfer from heated gases passing through the flow passage to the plate-like members defining such passage. Dimples (not shown) may be provided in the plate-like members defining flow passage 49 extending inwardly into such flow passage to decrease the velocity of gases moving through the passage and obtain more efiicient transfer of heat from such gases to the plate-like members. Each plate-like member 44, 43 has an edge portion which is dished laterally from the body portion and includes an outwardly extending flange 52 for member 44 and 53 for member 43. Each flange 52, 53 lies in a single plane and extends around the periphery of the plate-like member. Flanges 52, 53 of heat exchanger element 42 abut and are seam welded by machine weld ing processes to unite members 44, 43 into heat exchanger element 42 defining a flow passage for gases extending therein which is relatively large in cross sectional area at each end of the heat exchanger element and which is relatively small in cross sectional area through flow passage 49 of the heat exchanger element. Member 44 has flanges 54 and 55 on opposite ends which mate with the exteriors of housing 19 of flue tunnel 11 and housing 12 of firebox tunnel 10, respectively, and are connected thereto in conventional manner, as by spot welding or sheet metal screws with a gasket between the flange and the housing. Member 43 has flanges 56, 57 extending outwardly therefrom which are identical in all respects to the above described flanges 54, and are connected in the same manner as described therefor to flue tunnel 11 and firebox tunnel 10. As stated above, members 44, 43 of heat exchanger element 42 are identical in all respects and are exactly symmetrical about the common center line plane 27 of the firebox and flue tunnels. These are important features of the invention, because they result in only one die being necessary to make both halves of each heat exchanger element, there being no right hand and left hand halves to be joined together to form a heat exchanger element. As a consequence, great savings in manufacturing costs are effected. Another important feature of the heat exchanger elements is the peripheral flange lying in one plane, such as flanges 52, 53 for heat exchanger element 42, which permit the halves of each heat exchanger element to be joined together by highly eflicient machine welding rather than hand welding, with attendant considerable savings in manufacturing costs.

The housing 12 of firebox tunnel It) defines pairs of laterally aligned openings communicating between the interior of the firebox tunnel and the interior of each heat exchanger element seated on and partially surrounding the firebox tunnel. One such opening is indicated at 60 in FIG. 1, and it is to be understood that an identical opening is defined in the opposite side of housing 12 so that both openings communicate between the interiors of firebox tunnel 10 and the interior of heat exchanger element 41. Exactly similar pairs of openings communicate between the interior of firebox tunnel 10 and the interior of the other heat exchanger elements 49 and 42. As illustrated for the opening 6%), all of the openings are elongated and extend from adjacent the bottom of the firebox tunnel transversely to the longitudinal axis of the firebox tunnel to a point near the top of the firebox tunnel spaced slightly from the common center line plane 27. The elongate extent of opening 69 is transverse to the longitudinal axis of firebox tunnel 10. It is important that the opening 60 be elongated as described above for the reasons explained below. Housing 19 of flue tunnel 11 defines laterally aligned openings communicating between the interior of flue tunnel 11 and the interior chamher in each heat exchanger element. One of such openings is indicated at 61 in FIG. 1, and is to be understood that an identical opening is defined in the opposite side of housing 19 and aligned with opening 61 so that both openings communicate between the interior of flue tunnel 11 and heat exchanger element 41. Exactly similar pairs of openings are defined in housing 19 communicating between the interior of flue tunnel 11 and the interior of heat exchanger elements 40 and 42. As shown for opening 61, the opening is relatively large and encompasses a substantial portion of the side of housing 19 which is overlaid by heat exchanger element 41. An additional opening 62 is preferably defined in the bottom of housing 19 communicating between the interior of flue tunnel 11 and the interior of heat exchanger element 41. Opening 62 is generally rectangular and is symmetrical on each side of the common center line plane 27 of the flue tunnel and firebox tunnel. An opening the same as opening 62 is defined in housing 19 communicating between the interior of flue tunnel 11 and the interior of heat exchanger elements 40 and 42. It is apparent that with the three large openings communicating between the interior of flue tunnel 11 and the interior of each heat exchanger element, there is relatively unobstructed area for flow of gases from the interior of the heat exchanger elements to the interior of flue tunnel 11.

An elongated burner (FIG. 2) is disposed centrally I the several burner heads.

Within firebox tunnel l9 and rests in an arcuate recess 71 extending the elongate length of cover plate 15. As shown in FIG. 2, burner 75) is spaced from housing 12 of the firebox tunnel and is symmetrical on each side of common center line plane 27 of the firebox and flue tunnels. 3, 4, and 5. Referring to FIG. 3, burner 70 is comprised of identical halves '72, 73 which are generally semi-cylindrical in shape and which define outwardly extending peripheral flanges 74, 75 respectively. The halves 72, 73 are symmetrical so that one die can be used to make each half. Halves 72, 73 are joined together at the ends of burner '76 by seam. Welding flanges 74, 75 at 76, 77, and 78. Burner 70 defines plural pairs of aligned burner head openings, such as openings 79, 80, which receive the burner heads described below. The burner head openings communicate between the interior of burner 73 and the exterior thereof and the pairs of openings are spaced along the longitudinal extent of burner 79 the same amount as the spacing of the heat exchanger elements along the firebox and flue tunnels, so that when burner 79 is disposed in firebox tunnel 10, a pair of burner head openings is aligned with each heat exchanger element and with the openings, such as opening 60, communicating between the interior of the firebox tunnel and the interior of the heat exchanger elements. Spacing dimples such as 31, 82 are provided between flanges 74, 75 between the burner head openings to provide a gap between the flanges for propagation of flame in the burner in use. As illustrated in FIG. 5, each burner head opening includes an outwardly extending flange, such as flange 83, which receives a burner head and supports it. One end of burner 70 is closed at '76, but the other end of the burner is open at 84 for admission of gas and air through open end 84 to the interior of burner 7%. Halves 72, 73 of the burner are formed so that they define a constricted passageway at 85 between open end 84 of the burner and the first pair of burner head openings. Constricted passageway 85 flares outwardly to open end 84- so that it is a Venturi throat for mixing air-fuel gases admitted to the interior of burner 79 from open end 84 thereof. A Venturi throat extension 86 is connected at 87 to venturi throat 85 and extends inwardly in the interior chamber of burner 70 to open end 88 discharging therein. Venturi throat extension 86 has the same flow passage area as Venturi throat 85 at the connection 87 of the Venturi extension to the Venturi throat and flares outwardly at about 2 to open end 33 to provide for proper mixing of air-fuel gases admitted at open end 84 of the burner. As best shown in FIG. 5, the Venturi extension 86 is spaced from the walls of burner 7i) defining the interior chamber therein and is comprised of a pair of identical semi-cylindrical halves 89, 96 having outwardly extending flanges connected togther in conventional manner at 91 and )2. Open end 88 of Venturi extension 36 discharges into the interior chamber of burner 7% extending between such open end 88 and the closed end of the burner at connection 76, and this area within burner "7d defines an equalization plenum for equalization of gas pressures and proper distribution of the gaseous air-fuel mixture to The unique construction of Venturi extension 86 described above particularly its location within burner 70 in spaced relation from the walls defining the interior chamber in burner 70 and extending past the first pair or" burner head openings, is an important feature of the invention because the burner is considerably more compact and the furnace easier to install than conventional furnaces which include burners having the Venturi extension dischargim into the interior chamber in the burner at a point between the open end of the burner and the first pair or" burner head openings.

Burner heads 1%, H31 are disposed in and supported by burner head openings 79, 80 respectively. Each of the other burner head openings in burner 70 has a Burner 76 is shown in greater detail in FIGS burner head disposed in it and in similar manner, and all the burner heads are identical so that a description of one will suffice for all. Referring to FIG. 5, burner head 1% is comprised of a body 1%?2 defining a passageway 104 communicating between the interior of burner 70 and the exterior of the burner head. The top 1% of burner head 1% is spaced from the top of flange 83 on burner head opening 79 to aid in proper propagation of the flame from the burner head opening. A plurality of downwardly extending flanges, such as flange 105, are spaced along the bottom of the body of the burner head and bear on the bottom of flange 83 of burner head opening 79 to support the burner head in the burner head opening. A burner head grid 163 is connected to the exterior end of burner head 1% in conventional manner and defines a plurality of vertically elongated slots such as slot 187 (-FlG. 3) spaced from each other in the direction of the elongate extent of burner 70. in similar manner, burner head grid 103 defines a plurality of elongated slots extending between each supporting flange such as flange and spaced along the burner head grid in the direction of the elongate extent of the burner, such as slot 1%. The slots in the burner head grids, such as slots W7 and 1%, are elongated in a direction transverse to the elongate extent of burner 75 and lie in vertical planes at right angles to the common center-line plane 27 of the heat exchanger elements so that flame is emitted from the burner head in a fan-shaped pattern. This flame is emitted from the burner head grid and passes through the openings, such as opening 6i} in hou ing 19 or" the firebox tunnel into the enlarged lower portion of he heat exchanger element and on each side of the firebox tunnel so that, referring to FIG. 2, a fan-like flame symbolically indicated by dotted lines 15%, 151, 152, and 153 emanates from burner heads 1'51, 1&2 into heat exchanger element 42 on each side of firebox tunnel 10. The openings in housing 112 of the firebox tunnel are elongated as described above in order to accommodate this fan-shaped flame pattern. The above de scribed spacing between the top and bottom of the body of the burner head and the top and bottom of the flange on the burner head opening aids in the formation of this fan-shaped flame pattern. It is thus apparent that the lower enlarged portion of each heat exchanger element surrounding firebox tun-nel It! is substantially occupied by fan-shaped flames emanating from the burner head on each side of the burner aligned with the heat exchanger element and passing through the openings in the housing 19' of the firebox tunnel into the interior chamber in the heat exchanger element.

In operation, air which is to be heated by passing heat exchanger elements 49, 41, 42 may be directed past the heat exchanger elements either in a direction transverse to common center line plane 27 of the firebox and fine tunnels, in which case a top and bottom housing cover plate maybe secured on plates 28, 29* to aid in directionalizing such air flow, or alternatively such top and bottom cover plates may be omitted and the flow of air directed through the apparatus in a direction parallel to such common center line plane 27 or transverse to the elongate extents of the firebox and fine tunnels, in which case suitable housing side plates may be secured on the sides of plates 2-8, $9 to similarly aid in directionalizing such flow of air.

It is apparent from the above description that the inventive apparatus comprises a highly eflicient, compact heat exchanger which can be made with substantial savings in manufacturing costs and which permits flow of air through it in either a horizontal or a vertical direction.

We claim:

1. A furnace comprising an elongated tube-like firebox tunnel defining an interior burner chamber, an elongated tube-like flue tunnel defining an interior chamber for flow of gases, said flue tunnel being spaced from the firebox tunnel and parallel thereto and said firebox tunnel and flue tunnel being disposed with their longitudinal axes in a common plane and being symmetrical on each side of such plane, a plurality of plate-like heat exchanger elements extending between the firebox tunnel and the flue tunnel and extending laterally on each side of the firebox tunnel and flue tunnel, said heat exchanger elements being symmetrical on each side of the common plane of the longitudinal axes of the firebox tunnel and flue tunnel and being spaced from each other along the firebox tunnel and flue tunnel, each heat exchanger element comprising a pair of identical plate-like members having a central body portion and an edge portion circumscribing the body portion and dished laterally from the body portion to define an interior chamber in each heat exchanger element for flow of gases, an elongated burner disposed in the burner chamber of the firebox tunnel and extending approximately the length thereof, said burner defining an interior chamber extending its length and closed at one end of the burner and open at the other end of the burner, said burner defining plural pairs of laterally aligned burner head openings in opposite sides thereof communicating from the interior chamber of the burner to the exterior thereof with a pair of burner head openings aligned with the interior chamber of each heat exchanger element, a burner head disposed in each burner head opening and communicating from the interior chamber of the burner to the exterior of the burner head, said firebox tunnel defining openings communicating between the interior chamber in each heat exchanger element to each burner head to permit a flame to emanate from each burner head into the interior chamber of the heat exchanger elements on both sides of the firebox tunnel, and said flue tunnel defining a plurality of apertures communicating between its interior chamber and the interior chamber of each heat exchanger element for flow of gases from within each heat exchanger element to the interior chamber of the flue tunnel.

2. A furnace comprising an elongated tube-like firebox tunnel defining an interior burner chamber, an elon- .gated tube-like flue tunnel defining an interior chamber for flow of gases, said flue tunnel being spaced from the firebox tunnel and parallel thereto and said firebox tunnel and flue tunnel being disposed with their longitudinal axes in a common plane and being symmetrical on each side of such plane, a plurality of plate-like heat exchanger elements extending between the firebox tunnel and the flue tunnel and extending laterally on each side of the firebox tunnel and flue tunnel, said heat exchanger elements being symmetrical on each side of the common plane of the longitudinal axes of the firebox tunnel and flue tunnel and being spaced from each other along the firebox tunnel and flue tunnel, each heat exchanger element comprising a pair of identical plate-like members having a central body portion and an edge portion circumscribing the body portion and dished laterally from the body portion, the edge portion including a flange disposed along the edge portion and extending outwardly therefrom in a plane at right angles to the common plane of the longitudinal axes of the firebox tunnel and flue tunnel with the flange lying in a single plane, the flanges on each pair of plate-like members of a heat exchanger element being disposed in abutting engagement with each other to define an interior chamber in each heat exchanger element for flow of gases, means for connecting together the abutting flanges on each pair of plate-like members of each 'heat exchanger element, an elongated burner disposed in the burner chamber of the firebox tunnel and extending approximately the length thereof, said burner defining an interior chamber extending its length and closed at one end of the burner and open at the other end of the burner, said burner defining plural pairs of laterally aligned burner head openings in opposite sides thereof communicating from the interior chamber of the burner to the exterior thereof with a pair of burner head openings aligned with the interior chamber of each heat exchanger element, a constricted fiow passage defining a venturi throat disposed in the interior chamber of the burner adjacent the open end of such chamber and intermediate such open end and the first pair of burner head openings in the burner, a venturi throat extension extending from the throat of the venturi inwardly into the interior chamber of the burner in spaced relation from the walls of such chamber, said venturi throat extension defining a passage for flow of gases approximately equal to the constricted fioW passage through the venturi throat at the junction of the venturi throat extension and the venturi throat and gradually increasing in flow passage area to discharge into the interior chamber in the burner, the discharge end of the venturi throat extension being spaced from the closed end of the interior chamber of the burner and from the walls of such interior chamber to define a plenum mixing chamber for equalization of gas pressure, a burner head disposed in each burner head opening and communicating from the interior chamber of the burner to the exterior of the burner head, the portion of the burner head disposed in the burner head opening being spaced from the walls of the burner head opening, a burner grid on the discharge end of each burner head defining a piurality of enlongated apertures extending in the same direction as the extent of the heat exchanger elements between the firebox tunnel and the flue tunnel, said firebox tunnel defining openings communicating between the interior chamber in each heat exchanger element to each burner grid with each said opening extending from adjacent the bottom of the firebox tunnel to a point adjacent to the common plane of the longitudinal axes of the firebox tunnel and flue tunnel to define an elongated opening to permit a fan-shaped flame to emanate from each burner head into the interior chamber of the heat exchanger elements on both sides of the firebox tunnel, and said flue tunnel defining a plurality of apertures communicating between its interior chamber and the interior chamber of each heat exchanger element for flow of gases from within each heat exchanger element to the interior chamber of the flue tunnel.

3. A furnace comprising an elongated tube-like firebox tunnel defining an interior burner chamber, an elongated tube-like flue tunnel defining an interior chamber for flow of gases, said flue tunnel being spaced from the firebox tunnel and parallel thereto and said firebox tunnel and flue tunnel being disposed with their longitudinal axes in a common plane and being symmetrical on each side of such plane, a plurality of plate-like heat exchanger elements extending between the firebox tunnel and the flue tunnel and extending laterally on each side of the firebox tunnei and flue tunnel, said heat exchanger elements being symmetrical on each side of the common plane of the longitudinal axes of the firebox tunnel and the flue tunnel and being spaced from each other along the firebox tunnel and flue tunnel, each heat exchanger element comprising a pair of identical plate-like members having a central body portion and an edge portion circumscribing the body portion and dished laterally from the body portion, the edge portion including a flange disposed along the edge portion and extending outwardly therefrom in a plane at right angles to the common plane of the longitudinal axes of the firebox tunnel and flue tunnel with the flange lying in a single plane, the flanges on each pair of platelike members of a heat exchanger element being disposed in abutting engagement with each other to define an interior chamber in each heat exchanger element for flow of gases, means for connecting together the abutting flanges on each pair of plate-like members of each heat exchanger element, an elongated burner disposed in the burner chamber of the firebox tunnel and extending approximately the length thereof, said burner defining an interior chamber extending its length and closed at one end of the burner and open at the other end of the burner, said burner defining plural pairs of laterally aligned burner head openings in opposite sides thereof communicating from the interior chamber of the burner to the exterior thereof with a pair of burner head openings aligned with the interior chamber of each heat exchanger element, a burner head disposed in each burner head opening and communicating from the interior chamber of the burner to the exterior of the burner head, said firebox tunnel defining openings communicating between the interior chamber in each heat exchanger element to each burner head to permit a flame to emanate from each burner head into the interior chamber of the heat exchanger elements on both sides of the firebox tunnel, and said flue tunnel defining a plurality of apertures communicating between its interior chamber and the interior chamber of each heat exchanger element for flow of gases from Within each heat exchanger element to the interior chamber of the flue tunnel.

4. A furnace comprising an elongated tube-like firebox tunnel defining an interior burner chamber, an elongated tube-like flue tunnel defining an interior chamber for flow of gases, said flue tunnel being spaced from the firebox tunnel and parallel thereto and said firebox tunnel and flue tunnel being disposed With their longitudinal axes in a common plane and being symmetrical on each side of such plane, a plurality of plate-like heat exchanger elements extending between the firebox tunnel and the flue tunnel and extending laterally on each side of the firebox tunnel and flue tunnel, said heat exchanger elements being symmetrical on each side of the common plane of the iongitudinal axes of the firebox tunnel and the flue tunnel and being spaced from each other along the firebox tunnel and fine tunnel, each heat exchanger element comprising a pair of identical plate-like members having a central body portion and an edge portion circumscribing the body portion and dished laterally from the body portion to define an interior chamber in each heat exchanger element for flow of gases, said firebox tunnel defining openings communicating between the interior chamber in each heat exchanger element to the burner chamber in the firebox tunnel, and a pair of burner heads for each heat exchanger element communicating with said burner chamber and disposed laterally of said common plane to discharge a pair of lateral flames into the interiar chamber of each heat exchange element, and said flue tunnel defining a plurality of apertures communicating between its interior chamber and the interior chamber of each heat exchanger element for flow of gases from within each heat exchanger element to the interior chamber of the flue tunnel.

5. A furnace comprising an elongated tube-like firebox tunnel defining an interior burner chamber, an elongated tube-like flue tunnel defining an interior chamber for fiow of gases, said flue tunnel being spaced from the firebox tunnel and parallel thereto and said firebox tunnel and flue tunnel being disposed with their longitudinal axes in a common plane and being symmetrical on each side of such plane, a plurality of plate-like heat exchanger elements extending between the firebox tunnel and the flue tunnel and extending laterally on each side of the firebox tunnel and flue tunnel, said heat exchanger elements being symmetrical on each side of the common plane of the longitudinal axes of the firebox tunnel and flue tunnel and being spaced from each other along the firebox tunnel and flue tunnel, each heat exchanger element comprising a pair of identical plate-like members having a central body portion and an edge portion circumscribin-g the body portion and dished laterally from the body portion, the edge portion including a flange disposed along the edge portion and extending outwardly therefrom in a plane at right angles to the common plane of the longitudinal axes of the firebox tunnel and flue tunnel with the flange lying in a single plane, the flanges on each pair of plate-like members of a heat exchanger element being disposed in abutting engagement with each other to define an interior chamber in each heat exchanger element for flow of gases, means for connecting together the abutting flanges on each pair of plate-like members of each heat exchanger element, said firebox tunnel defining openings communictab ing between the interior chamber in each heat exchanger element to the burner chamber in the firebox tunnel, and a pair of burner heads for each heat exchanger element communicating with said burner chamber and disposed laterally of said common plane to discharge a pair of lateral flames into the interior chamber of each heat exchange element, and said flue tunnel defining a plurality of apertures communicating between its interior chamber and the interior chamber of each heat exchanger ele ment for flow of gases from within each heat exchanger element to the interior chamber of the flue tunnel.

References tCited in the file of this patent UNITED STATES PATENTS 1,189,094 Goodwin June 27, 1916 1,596,452 Reeves et a1 Aug. 17, 1926 1,873,570 Frantz Aug. 23, 1932 FOREIGN PATENTS 104,821 Australia Nov. 25, 1926 7,575 Great Britain of 1907 

1. A FURNACE COMPRISING AN ELONGATED TUBE-LIKE FIREBOX TUNNEL DEFINING AN INTERIOR BURNER CHAMBER, AN ELONGATED TUBE-LIKE FLUE TUNNEL DEFINING AN INTERIOR CHAMBER FOR FLOW OF GASES, SAID FLUE TUNNEL BEING SPACED FROM THE FIREBOX TUNNEL AND PARALLEL THERETO AND SAID FIREBOX TUNNEL AND FLUE TUNNEL BEING DISPOSED WITH THEIR LONGITUDINAL AXES IN A COMMON PLANE AND BEING SYMMETRICAL ON EACH SIDE OF SUCH PLANE, A PLURALITY OF PLATE-LIKE HEAT EXCHANGER ELEMENTS EXTENDING BETWEEN THE FIREBOX TUNNEL AND THE FLUE TUNNEL AND EXTENDING LATERALLY ON EACH SIDE OF THE FIREBOX TUNNEL AND FLUE TUNNEL, SAID HEAT EXCHANGER ELEMENTS BEING SYMMETRICAL ON EACH SIDE OF THE COMMON PLANE OF THE LONGITUDINAL AXES OF THE FIREBOX TUNNEL AND FLUE TUNNEL AND BEING SPACED FROM EACH OTHER ALONG THE FIREBOX TUNNEL AND FLUE TUNNEL, EACH HEAT EXCHANGER ELEMENT COMPRISING A PAIR OF IDENTICAL PLATE-LIKE MEMBERS HAVING A CENTRAL BODY PORTION AND AN EDGE PORTION CIRCUMSCRIBING THE BODY PORTION AND DISHED LATERALLY FROM THE BODY PORTION TO DEFINE AN INTERIOR CHAMBER IN EACH HEAT EXCHANGER ELEMENT FOR FLOW OF GASES, AN ELONGATED BURNER DISPOSED IN THE BURNER CHAMBER OF THE FIREBOX TUNNEL AND EXTENDING APPROXIMATELY THE LENGTH THEREOF, SAID BURNER DEFINING AN INTERIOR CHAMBER EXTENDING ITS LENGTH AND CLOSED AT ONE END OF THE BURNER AND OPEN AT THE OTHER END OF THE BURNER, SAID BURNER DEFINING PLURAL PAIRS OF LATERALLY ALIGNED BURNER HEAD OPENINGS IN OPPOSITE SIDES THEREOF COMMUNICATING FROM THE INTERIOR CHAMBER OF THE BURNER TO THE EXTERIOR THEREOF WITH A PAIR OF BURNER HEAD OPENINGS ALIGNED WITH THE INTERIOR CHAMBER OF EACH HEAT EXCHANGER ELEMENT, A BURNER HEAD DISPOSED IN EACH BURNER HEAD OPENING AND COMMUNICATING FROM THE INTERIOR CHAMBER OF THE BURNER TO THE EXTERIOR OF THE BURNER HEAD, SAID FIREBOX TUNNEL DEFINING OPENINGS COMMUNICATING BETWEEN THE INTERIOR CHAMBER IN EACH HEAT EXCHANGER ELEMENT TO EACH BURNER HEAD TO PERMIT A FLAME TO EMANATE FROM EACH BURNER HEAD INTO THE INTERIOR CHAMBER OF THE HEAT EXCHANGER ELEMENTS ON BOTH SIDES OF THE FIREBOX TUNNEL, AND SAID FLUE TUNNEL DEFINING A PLURALITY OF APERTURES COMMUNICATING BETWEEN ITS INTERIOR CHAMBER AND THE INTERIOR CHAMBER OF EACH HEAT EXCHANGER ELEMENT FOR FLOW OF GASES FROM WITHIN EACH HEAT EXCHANGER ELEMENT TO THE INTERIOR CHAMBER OF THE FLUE TUNNEL. 